1. Field of the Invention
The present invention relates to an ink jet printing apparatus, more particularly, it relates to a full-line type ink jet printing apparatus.
2. Description of the Related Art
An ink jet printing apparatus performs printing by ejecting ink from ejection ports of a print head. As an energy generating element for generating energy for ejecting ink, an electro-machinery converter such as a piezoelectric element, and an element are employed that generates heat by irradiating electromagnetic waves such as a laser to eject ink droplets by the heat. Additionally, an electro-thermal converting element having a heat generation resistance for heating liquid is employed.
In particular, ejection ports can be arranged at high density in a print head for ejecting ink droplets with use of thermal energy, and therefore printing can be performed at high resolution.
The print head employing the electro-thermal converting element as the energy generating element can be easily downsized. Recently, advantages in IC technology and micro-processing technology can be used that remarkably advance technology and improve reliability in the semiconductor industry whereby high density mounting can be easily realized, and manufacturing costs can be saved. Additionally, in order to perform printing at higher definition, a method has been recently employed that creates the ejection ports for ejecting ink at high precision with use of photo-lithography technology.
In order to print a high definition image at higher speeds, a print head having a longer print width has been recently desired. Specifically, a print head having a length of 4 to 13 inch has been desired. As such a long print head, a print head, in which a plurality of print element boards and discrete filters corresponding thereto are arranged on a support substrate and an ink flow path is formed, is disclosed as prior art in Japanese Patent Laid-Open No. 2005-144919.
A common liquid chamber is provided on the ink flow path in the long print head, and discrete liquid chambers are included for storing ink to be supplied from the common liquid chamber to the print element boards each having a plurality of ejection port groups. Additionally, discrete filters and discrete gas-liquid separation members are arranged in the print head. In such a long print head, the ink is circulated and supplied from an ink flow-in port to an ink flow-out port through the common liquid chamber so as to be supplied to the common liquid chamber.
Such ink circulation and supply to the common liquid chamber is performed by simultaneous operation of a circulation pressurization pump and a circulation suction pump. For example, in Japanese Patent Laid-Open No. 8-244250 (1996), P1=P2 is disclosed as a relationship between P1 and P2, wherein P1 and P2 represent flow rates of the circulation pressurization pump and the circulation suction pump respectively. According to this relationship, the circulating ink is not discharged from the ejection port by pressure.
However, bubble to be generated in ink supply, etc., is accumulated in the discrete liquid chamber which is a space formed by being surrounded with each print element board and the discrete filters, the bubble causes clogging of the ejection port in printing, and the ink is not sufficiently ejected at times. Thus, the bubble is sometimes removed from the discrete liquid chamber by operating an air suction pump during the ink circulation. When the flow rates of the circulation pressurization pump and the circulation suction pump are kept the same, the ink in the common liquid chamber hardly flows into each discrete liquid chamber. In this case, operation for removing the bubble in the discrete liquid chamber cannot be performed, and clogging of the ejection port cannot be removed.